X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplEnv.lhs;h=245f313e8f874b4f59f60e26f2dd5ca2a26ba5cc;hb=84923cc7de2a93c22a2f72daf9ac863959efae13;hp=c9fb4fbb8ba23d5d9471a535c0498c71fe0609e1;hpb=6f074a37a1546391632863898da3c32bbb7995df;p=ghc-hetmet.git

diff --git a/compiler/simplCore/SimplEnv.lhs b/compiler/simplCore/SimplEnv.lhs
index c9fb4fb..245f313 100644
--- a/compiler/simplCore/SimplEnv.lhs
+++ b/compiler/simplCore/SimplEnv.lhs
@@ -608,8 +608,12 @@ substLetIdBndr :: SimplEnv -> InBndr 	-- Env and binder to transform
 	       -> (SimplEnv, OutBndr)
 -- C.f. substIdBndr above
 -- Clone Id if necessary, substitute its type
--- Return an Id with completely zapped IdInfo
+-- Return an Id with its fragile info zapped
+--	namely, any info that depends on free variables
 -- 	[addLetIdInfo, below, will restore its IdInfo]
+--	We want to retain robust info, especially arity and demand info,
+--	so that they are available to occurrences that occur in an
+--	earlier binding of a letrec
 -- Augment the subtitution 
 --	if the unique changed, *or* 
 --	if there's interesting occurrence info
@@ -620,7 +624,10 @@ substLetIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) old
   where
     id1	   = uniqAway in_scope old_id
     id2    = substIdType env id1
-    new_id = setIdInfo id2 vanillaIdInfo
+
+    -- We want to get rid of any info that's dependent on free variables,
+    -- but keep other info (like the arity).
+    new_id = zapFragileIdInfo id2
 
 	-- Extend the substitution if the unique has changed,
 	-- or there's some useful occurrence information